1. Field of the Invention
The subject invention relates generally to electronic circuitry for use in the medical field and, more particularly, to an active analog circuit for connection to a single thermistor to cause the combination analog circuit and thermistor to exhibit a characteristic like that of a two-thermistor circuit.
2. Description of Related Art
Use of disposable temperature probes for single patient application is common today because of the high cost of cleaning and resterilizing medical products. The well-known 700 series disposable temperature probe is considerably more costly than single thermistor disposable temperature probes. Most of the additional cost of the 700 series probe is attributable to the cost of the sensor element of the probe, which employs two thermistors.
Unfortunately, manufacturers of patient monitors continue to make monitors which use only the 700 series, dual thermistor probes. Users of such patient monitors are forced to purchase 700 series probes or an electronic adapter. The typical electronic adapter accepts signals from a low cost thermocouple-type probe and simulates the resistances of the 700 series thermistor elements. This type of electronic adapter invariably uses a microprocessor, analog-to-digital converter, and some sort of digital-to-analog conversion to perform its function. The net result is a complex, high-cost device requiring maintenance for batteries and calibration. While such an adapter allows use of low cost thermocouple probes, it also adds the cost of maintenance, battery replacement, and calibration, as well as introducing its own errors to the temperature monitoring procedure.
Some users have a mix of instruments and are currently purchasing both 400 and 700 series thermistors or converting thermocouple signals through electronic adapters. It would prove far more convenient for such users to purchase only less expensive 400 series disposable probes for connection to their 700 series instruments. Their 400 series instruments would continue to accept a direct connection to the 400 series probes.